Convertibles are often equipped with a movable convertible top, which can be automatically moved for example from an open to a closed position or vice versa with the press of a button. The movement of the convertible top is usually effected by a hydraulic drive, which in turn drives a convertible top mechanism, which includes a convertible top linkage. The convertible top linkage may be a carrying device for a textile roof as well as a so-called hard-top folding roof with mainly rigid roof elements, and may include a cover for a convertible top compartment as well as all elements that are being moved in the process. To control the movement of the convertible top it is necessary to obtain information on the current position of the convertible top.
German Patent Application DE19842337A1 describes an operating mechanism for a folding top of a convertible vehicle, comprising a hydraulic gear with a hydraulic pump and hydraulic motors that are linked to the foldable top, whereby the operating mechanism comprises a position transmitter for generating electric signals according to positions of the folding top and control electronics for creating the planned movement of the convertible top and for sensing the electric signals of the position transmitter. Limit switches are positioned at the ends of the range of motion of the convertible top as well as within the range of motion of the convertible top; they are used to sense the convertible top position. The limit switches transmit a signal to the control electronics as soon as the convertible top has reached the final position switch. In the process, a constant rotational speed or a constant power output of the electric motor that drives the hydraulic pump is allocated to each area between the two final position switches.
The limit switches are used as terminal points for position recognition. To determine the position of the convertible top between these terminal points it is suggested to integrate the rotational speed of the motor over time and to interpolate the convertible top position. To avoid a high quantity of limit switches, the DE19842337A1 application proposes to calculate the approximate position of the convertible top with the help of the control equipment using the number of revolutions of the electric motor and the average displacer volume of the hydraulic pump.
However, the disadvantage of using this method is that only the theoretical, mathematically calculated information on the convertible top position is available between the terminal points with limit switches. The information does no longer corresponds to the actual convertible top position for example after a change in speed of the convertible top movement. Moreover, the disadvantage of this solution is that a number of end switches have to be provided in the range of motion of the convertible top to enhance the accuracy of the information in regard to the current convertible top position and that this involves an accordingly higher amount of expense.
According to the DE19842337A1, also sensors for sensing the positioning angle or travel distance of the convertible top linkage may be used in order to accurately calculate the current position of the convertible top, whereby the sensors create an analog signal or they scan and count marks on the linkage like a potentiometer for example.
However, these types of sensors that are designed as potentiometers and are used to continuously scan the displacement have to be directly attached to the pivot point of the convertible top section that is to be scanned, whereby it is problematic that the cumbersome size of the potentiometer, because of its physical properties, can not fall below a certain limit. As a result, there is the danger of collision between the sensors and other convertible top segments when these types of sensors are being used.
Moreover, this type of sensor that is designed as a potentiometer is a manual part, which is subject to wear when it is used, and to a drift in temperatures, which can lead to errors in regard to the information on the current convertible top position.
It is also known from practical applications that the convertible top position can be calculated with the aid of the measurement of the retraction travel of the cylinders of a hydraulic system of the convertible top drive. However, it has to be taken into account with this method, that this type of solution requires a comparably large installation space and does not provide any information on the position of the convertible top inherently, but merely on the distance of cylinder travel. Therefore, a possibly defective connection point, that is, a disruption of the connection between a cylinder and the convertible top linkage, cannot be detected.
The fact that the currently known installations for the recognition of convertible top positions are highly prone to errors is disadvantageous in particular in regard to the detection of an obstruction situation, since possible problems during the sequence of the convertible top motion, such as a decelerated motion or the blocking of the convertible top, which can be indications that an object or a body part is caught in the convertible top mechanism, may not be detected or not detected until very late.